There is a conventionally known powered sliding device for a vehicle sliding door for sliding the sliding door in a door-opening direction and a door-closing direction by rotating a wire drum coupled to the sliding door through a wire cable by motive power of a motor, the sliding door which has been moved to a door-open position by the sliding device is retained in the open position by a door holder.
As the door holder, there are a mechanically engaging holder using a latch/ratchet mechanism and a striker and a climbing-over holder using an elastic ridge such as a leaf spring or a non-elastic ridge. In a case of the climbing-over holder, if the sliding door is slid in the opening direction, the sliding door comes into contact with the door holder, climbs over the door holder against climbing-over resistance of the door holder, reaches the open position, and then is retained in the open position by the climbing-over resistance of the door holder. A door retaining force of the climbing-over holder is equal to an intensity of the climbing-over resistance and generally set at such an intensity as to be able to retain the sliding door in the open position even when a vehicle body is inclined about 15 degrees. The door retaining force stronger than this is believed to impair operability in sliding the sliding door.
The open-position is set between a mechanical door-opening end position of the sliding door and a climbing-over position of the door holder and has a width of about 20 mm to 40 mm.
There are some problems in the powered sliding device using the climbing-over holder.
The first problem is that play of about 20 mm to 40 mm of the open position adversely affects the retaining force of the door holder which is set to be able to bear the inclination of about 15 degrees. In general, when the sliding door climbs over the door holder and moves to the door-opening end position by motive power of the powered sliding device, the sliding door is released from the sliding device. At this time, if the vehicle body is in a nose-down inclined state, the sliding door gradually slides a distance of the play of 20 mm to 40 mm in the closing direction under influence of the inclination and comes into contact with the door holder while having an inertial force in the closing direction. The sliding door having the inertial force may climb over the door holder and get out of the open position in some cases even when the inclination of the vehicle body is smaller than 15 degrees.
There is a powered sliding device for solving this problem as proposed in Japanese Patent Application Laid-open No. 11-301271. In this powered sliding device, a weak breaking force is applied to the sliding door for a while after the sliding door has been moved to the door-opening end position by motive power to thereby prevent application of a strong inertial force to the sliding door.
In this powered sliding device, however, the sliding door is intermittently coupled to a motor by repeatedly turning on and off an electromagnetic clutch to thereby apply the weak braking force to the sliding door. Therefore, even after the sliding door has been moved to the door-opening end position, it is impossible to manually move the sliding door for a while. Moreover, because the braking force is applied to the sliding door irrespective of the inclined state of the vehicle body, a user sometimes feels a sense of discomfort. In other words, the sliding door does not move irrespective of presence or absence of the braking force when the vehicle body is not inclined and this sliding door which does not move strongly impresses the user with completion of door opening operation. Therefore, the user may be given an illusion that the door can be closed manually before completion of the braking operation.
The second problem in the climbing-over door holder is that the door holder has a property of increasing a sliding speed of the sliding door in addition to a property of reducing the sliding speed. In other words, the door holder functions as resistance to movement of the sliding door until the sliding door passes a center of the door holder while the door holder pushes the sliding door out after the sliding door has passed the center of the door holder. Therefore, the sliding door may slide at an unexpectedly high speed in closing the sliding door by manual operation. This phenomenon becomes more pronounced when the vehicle body is in the nose-down inclined state.
Moreover, the property of pushing out the sliding door adversely affects the sliding movement of the sliding door even in closing the sliding door with the motive power of the motor, it is difficult to make the sliding speed constant, and smoothness of the sliding movement is significantly impaired especially when the vehicle body is in the nose-down inclined state.
The third problem in the climbing-over door holder is that the sliding door climbs over the door holder from the open position and moves in the closing direction if an external force greater than the retaining force of the door holder acts on the sliding door. Most of such external forces are applied by the manual operation by the user, but the external force may act on the sliding door due to vehicle braking operation during running of an automobile. The external force applied by the braking operation is unexpectedly large. At a vehicle speed as low as 3 km/h, the sliding door may climb over the door holder from the open position and close due to the external force applied by the braking operation in some cases. Therefore, it is necessary to pay close attention to move the vehicle when the sliding door is open.